Feature: `output` matcher

  The `output` matcher provides a way to assert that the block has emitted content to either
  `$stdout` or `$stderr`.

  With no arg, passes if the block outputs `to_stdout` or `to_stderr`. With a string, passes
  if the blocks outputs that specific string `to_stdout` or `to_stderr`. With a regexp or
  matcher, passes if the blocks outputs a string `to_stdout` or `to_stderr` that matches.

  Note: `to_stdout` and `to_stderr` work by temporarily replacing `$stdout` or `$stderr`, so
  they're not able to intercept stream output that explicitly uses `STDOUT`/`STDERR` or that
  uses a reference to `$stdout`/`$stderr` that was stored before the matcher is used.

  To capture output from any spawned subprocess as well, use `to_stdout_from_any_process`
  or `to_stderr_from_any_process`. Output from any process that inherits the main process's
  corresponding standard stream will be captured.

  Note: `to_stdout_from_any_process` and `to_stderr_from_any_process` use tempfiles to
  capture output, and are thus significantly (~30x) slower than `to_stdout` and `to_stderr`.

  Scenario: Using the `output_to_stdout` matcher
    Given a file named "output_to_stdout_spec.rb" with:
      """ruby
      RSpec.describe "output.to_stdout matcher" do
        specify { expect { print('foo') }.to output.to_stdout }
        specify { expect { print('foo') }.to output('foo').to_stdout }
        specify { expect { print('foo') }.to output(/foo/).to_stdout }
        specify { expect { }.to_not output.to_stdout }
        specify { expect { print('foo') }.to_not output('bar').to_stdout }
        specify { expect { print('foo') }.to_not output(/bar/).to_stdout }

        # deliberate failures
        specify { expect { }.to output.to_stdout }
        specify { expect { }.to output('foo').to_stdout }
        specify { expect { print('foo') }.to_not output.to_stdout }
        specify { expect { print('foo') }.to output('bar').to_stdout }
        specify { expect { print('foo') }.to output(/bar/).to_stdout }
      end
      """
    When I run `rspec output_to_stdout_spec.rb`
    Then the output should contain all of these:
      | 11 examples, 5 failures                                      |
      | expected block to output to stdout, but did not              |
      | expected block to not output to stdout, but output "foo"     |
      | expected block to output "bar" to stdout, but output "foo"   |
      | expected block to output "foo" to stdout, but output nothing |
      | expected block to output /bar/ to stdout, but output "foo"   |

  Scenario: Using the `output_to_stderr` matcher
    Given a file named "output_to_stderr.rb" with:
      """ruby
      RSpec.describe "output_to_stderr matcher" do
        specify { expect { warn('foo') }.to output.to_stderr }
        specify { expect { warn('foo') }.to output("foo\n").to_stderr }
        specify { expect { warn('foo') }.to output(/foo/).to_stderr }
        specify { expect { }.to_not output.to_stderr }
        specify { expect { warn('foo') }.to_not output('bar').to_stderr }
        specify { expect { warn('foo') }.to_not output(/bar/).to_stderr }

        # deliberate failures
        specify { expect { }.to output.to_stderr }
        specify { expect { }.to output('foo').to_stderr }
        specify { expect { warn('foo') }.to_not output.to_stderr }
        specify { expect { warn('foo') }.to output('bar').to_stderr }
        specify { expect { warn('foo') }.to output(/bar/).to_stderr }
      end
      """
    When I run `rspec output_to_stderr.rb`
    Then the output should contain all of these:
      | 11 examples, 5 failures                                      |
      | expected block to output to stderr, but did not              |
      | expected block to not output to stderr, but output "foo      |
      | expected block to output "bar" to stderr, but output "foo\n" |
      | expected block to output "foo" to stderr, but output nothing |
      | expected block to output /bar/ to stderr, but output "foo\n" |

  Scenario: Using the `output_to_stdout_from_any_process` matcher
    Given a file named "output_to_stdout_from_any_process_spec.rb" with:
      """ruby
      RSpec.describe "output.to_stdout_from_any_process matcher" do
        specify { expect { system('printf foo') }.to output.to_stdout_from_any_process }
        specify { expect { system('printf foo') }.to output("foo").to_stdout_from_any_process }
        specify { expect { system('printf foo') }.to output(/foo/).to_stdout_from_any_process }
        specify { expect { }.to_not output.to_stdout_from_any_process }
        specify { expect { system('printf foo') }.to_not output("bar").to_stdout_from_any_process }
        specify { expect { system('printf foo') }.to_not output(/bar/).to_stdout_from_any_process }

        # deliberate failures
        specify { expect { }.to output.to_stdout_from_any_process }
        specify { expect { }.to output('foo').to_stdout_from_any_process }
        specify { expect { system('printf foo') }.to_not output.to_stdout_from_any_process }
        specify { expect { system('printf foo') }.to output('bar').to_stdout_from_any_process }
        specify { expect { system('printf foo') }.to output(/bar/).to_stdout_from_any_process }
      end
      """
    When I run `rspec output_to_stdout_from_any_process_spec.rb`
    Then the output should contain all of these:
      | 11 examples, 5 failures                                      |
      | expected block to output to stdout, but did not              |
      | expected block to not output to stdout, but output "foo"     |
      | expected block to output "bar" to stdout, but output "foo"   |
      | expected block to output "foo" to stdout, but output nothing |
      | expected block to output /bar/ to stdout, but output "foo"   |

  Scenario: Using the `output_to_stderr_from_any_process` matcher
    Given a file named "output_to_stderr_from_any_process_spec.rb" with:
      """ruby
      RSpec.describe "output.to_stderr_from_any_process matcher" do
        specify { expect { system('printf foo 1>&2') }.to output.to_stderr_from_any_process }
        specify { expect { system('printf foo 1>&2') }.to output("foo").to_stderr_from_any_process }
        specify { expect { system('printf foo 1>&2') }.to output(/foo/).to_stderr_from_any_process }
        specify { expect { }.to_not output.to_stderr_from_any_process }
        specify { expect { system('printf foo 1>&2') }.to_not output("bar").to_stderr_from_any_process }
        specify { expect { system('printf foo 1>&2') }.to_not output(/bar/).to_stderr_from_any_process }

        # deliberate failures
        specify { expect { }.to output.to_stderr_from_any_process }
        specify { expect { }.to output('foo').to_stderr_from_any_process }
        specify { expect { system('printf foo 1>&2') }.to_not output.to_stderr_from_any_process }
        specify { expect { system('printf foo 1>&2') }.to output('bar').to_stderr_from_any_process }
        specify { expect { system('printf foo 1>&2') }.to output(/bar/).to_stderr_from_any_process }
      end
      """
    When I run `rspec output_to_stderr_from_any_process_spec.rb`
    Then the output should contain all of these:
      | 11 examples, 5 failures                                      |
      | expected block to output to stderr, but did not              |
      | expected block to not output to stderr, but output "foo"     |
      | expected block to output "bar" to stderr, but output "foo"   |
      | expected block to output "foo" to stderr, but output nothing |
      | expected block to output /bar/ to stderr, but output "foo"   |
